1. Field of Invention
This invention relates to lasers and more particularly to solid state lasers.
2. Prior Art
In solid state lasers the laser cavity supports lasing action in a direction parallel to the laser junction, or to the active layer in a double hetereostructure laser. If one of the cavity mirrors is made partially transmissive the radiation will exit substantially normal to the mirrored surface, with the known divergence. If lasers are to be organized in a matrix array and fabricated in gross by successive formation of the necessary electrodes and semiconducting layers with subsequent isolation into individual lasing islands, the normal direction of the exiting radiation somewhat limits the utility of the array. To add mirrors or refractive devices to divert the exiting rays complicates the structure. Prior workers in the field have formed periodic gratings in the surface of a solid state laser. While this does provide coupling out normal to the junctions in the laser, it necessitates a hole in the electrodes or the use of transparent electrodes. Furthermore, the fabrication of the grating in the laser chip may create defect centers to prejudice the life of the laser.
Grating coupled lasers per se are described by D. R. Scifres et al in Applied Physics Letters, Vol. 26, No. 2, Jan. 15, 1975, p48, and by Kazarinov et al in Soviet Physics--Semiconductors, Vol. 6, No. 7, January 1973, p1184. Zory and Comerford in an article entitled "Grating--Coupled Double Heterostructure AlGaAs Diode Lasers," Institute of Electrical and Electronics Engineers Inc. Annals No. 507QE014 also describe the normal to the junction coupling out of laser radiation by means of gratings.
To overcome the drawbacks discussed above the instant invention leaves the solid state laser intact and effects the feedback and coupling out by means of a grating coupled waveguide. This obviates the risk of causing defect centers in the laser and eliminates the necessity for specially constructed electrodes, thus permitting optimum pumping efficiency.